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FUR'IHER EXPERIMENTS IN THE DEVELOPMENT
OF ENGINEERING METHODS FOR THE CONTROL

CIF‘ LOCBE SMUT IN UHEAT

by
George Eli Cheklich
v

An Abstract

Suhnitted to the School of Graduate Studies of Michigan
State College of Agriculture and Applied Science
in partial fulfillment of the requirements

for the degree of
MASTER OF SCIENCE

Department of Agricultural Engineering

1953

Approved p g M

FURIHER.EXFERIMENTS IN THE DEVELOPMENT
OF ENGINEERING METHODS FOR THE CONTROL

OF LOOSE SMUT IN WHEAT

Loose smut of wheat causes an estimated total annual loss to the

farmers of the United States, of more than eleven million bushels.

Since loose smut is an internally seed-borne fungus, it is necessary

to employ a treatment which will penetrate the wheat seed and kill the
loose smut fungus, without affecting the wheat germ. At present, the
only treatments known to be effective in the control of this disease

are the various hot water treatments. Hot water treatments are difficult
and tedious to apply and require close temperature control. The main
objection to the hot water treatments is that the seed is wetted during
treatment.

Because of the aforementioned disadvantages of the hot water treat-
ments, there appeared to be a need for a dry treatment. In previous
investigations infected seed was treated with infrared radiation and
dielectric heat. Infrared radiation was found to be the more practicable
treatment.

This study is in part, a further investigation of the infrared
treatment. An infrared heat lamp was used as a source of infrared radia-
tion. Results of field tests with infrared treated seed indicate that
the infrared treatment may be effective in the control of this disease.
However, because of a number of contributing factors, considerable diffi-
culty was encountered in reproducing the infrared treatments. These

‘) (‘1 p (‘4‘) ‘
t_)“ki "\js)_1.

factors are: (l) influence of air currents, (2) uncontrollable exposure
of the wheat embryo during treatment, and (3) variations in atmospheric
absorption of infrared radiation.

Subsequently, the effects of treating wheat in an electric oven
were investigated. A number of samples of wheat were oven treated and
planted in the greenhouse. Results from these tests indicate a trend of
decreasing loose smut incidence in those samples treated above 98°C. for
a period of more than thirty minutes. An investigation of this treat-—
ment using a much larger number of plants is necessary to determine the

Optimal conditions under which loose smut of wheat can be controlled.

FURTHER.EXFERIMENTS IN THE DEVELOPMENT
OF ENGINEERING-METHODS FOR THE CONTROL

OF LOOSE SMUT IN HHEAT

by
George Eli Cheklich

A Thesis

Submitted to the School of Graduate Studies of Michigan
State College of Agriculture and Applied Science
in partial fulfillment of the requirements

for the degree of

MASTER OF SCIENCE

Department of Agricultural Engineering

1953

ACKNOWLEDGMENTS

The author wishes to express sincere appreciation and gratitude
to the following:

Doctor E. H. Lucas for his guidance and many helpful suggestions
throughout the course of this study.

Professor D. It Wiant for his aid and advice in carrying out
this investigation.

Professor H. M. Brown for his counsel in the statistical evaluation
of the eXperimental results.

Professors I. B. Baccus and R. J. Jeffries for their cooperation

and advice.

11

TABLE OF CONTENTS

INTREDUCTION .....................................................
REVIEW OF LITERATURE .............................................
The Nature of Loose Smut ....................................
Methods of Treatment Previously Used ........................

Hot Hater Treatments ...................................

Previous Treatments'With Infrared Radiation ............

Treatment By Dielectric Heating ........................

TREATMENT WITH INFRARED RADIATION ................................
Objectives ..................................................
Apparatus and Equipment .....................................
Experimental Procedure ......................................
Field Tests .................................................
Factors Affecting Reproduceability of Infrared Treatments ...
TREATMENT‘HITH OVEN'HEAT .........................................
Objectives ..................................................
Apparatus and Equipment .....................................
Experimental Procedure ......................................
Greenhouse Tests ............................................

SW! ......OOOOOCOO......OCOOOOOOOOOO.........OOOOOOOOOOOOOOOOO

LIST G. REERENCE‘S .......OOOOOOOOOOOOOO0.00.00.00.00...0.0.000...

Page

10
13
15
l7
17
20
26

39

45
47
L8
58
59

Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Figure 9
Figure 10
Figure 11

iii

LIST OF FIGURES

Wheat heads showing appearance and develOpment of

10083 smut ......OOOOOOOO0.0.0.........OOOOOOOOOOOOOOOOO
smcme Of the Wheat mm .....OOOOOOOOOOOOOOOOOO....
Electromagnetic spectrum showing the infrared region ...

wavelength distribution of a 250~watt infrared

heat lamp ..............................................
Energy distribution of a 250dwatt infrared heat lamp ...
Infrared heating apparatus .............................
Temperature measuring device used in infrared tests ....
Rate of heat loss from temperature measuring device ....
Cenco Electric vacuum Oven .............................

Effect of temperature on germination of Illinois 1-128
"heat for ‘ onfihmr fluent O......OOOOCOOOCOCOOOOOOO

Oven treated wheat growing in a greenhouse bench .......

Page

18

21
21

22

25

46

49
52

 

Table

Table

Table .

Table
Table

Table

Table
Table
Table

Table

Table

Table

Table

axmhwto

\l

10

12
13

iv

LIST (F TABLES

Results of detection of loose smut mycelium in the
seedlings of spring wheat Illinois 1—128 ..................

Effect of sudden cooling after treatment, on germination ..
Effect of varying lamp heights on germination .............
Field test results from infrared treatments ...............
Summary of field tests ....................................

Frequency distribution by treatment number, of field

reenlts 000000000000000000000000000000000000000000000000000
Analysis of variance of field emergence results ...........
mais 0f variance 0f field amt reSUltS 0.00000000000000
AnalySis Of covariance Of field results 0000000000000000000
Effect of different percentages of relative humidity on
the temperatures attained for a 10-inch lamp height, and
3-5 Minute treatment O0.00............OOOOOOOOO.....OOOOOOO
Effect of a one-hour treatment at varying temperatures on
germination and weight of radicles after a 72-hour
germination periOd ......OOOOOOOOOOO......OOOOOOOOOOOOOOOOO

Treatments for greenhouse tests ...........................

Emergence and smut results from greenhouse tests ..........

Table 147 Frequency distribution by treatment number, of the

Table

Table
Table

15

16
17

results from greenhouse tests .............................

Analysis of variance of emergence results from greenhouse

teStS 0....00.00000........OOOOOOOOOOOO.....OOOOIOOOOO.....
Summary of emergence results from greenhouse tests ........

Summary of smut results from greenhouse tests .............

30
32
34

35
36
36
37

41

5O
51

53

55

56
57
57

INTRODUCTION

Loose smut is one of the commonly known destructive diseases of
wheat. According to estimates compiled by the Bureau of Plant Industry,
the average annual loss to farmers of the United States resulting from
this disease is more than 11,000,000 bushels. While this loss is not as
great as that resulting from other diseases of wheat, it is a considerable
amount and certainly warrants some attention.

Loose smut infected plants appear to be normal during the growing
season. It is only during the flowering stage of the growing cycle that
loose smut can be detected. At this time, the infected heads appear as a
black mass of smut spores instead of normal heads. The infestation has
been known to be as high as 40 percent. Usually all the heads from av
diseased.plant are infected. The yield would therefore be lowered because
of a reduction in the number of normal plants.

Because loose smut is an internally borne fungus, it cannot be con-
trolled by treating with surface disinfectants as can other smuts of wheat.
It can be controlled only by a treatment which in some way penetrates the
wheat kernel and kills the loose smut fungus without affecting the embryo.
Hot-water treatments are the only generally recommended.preventive measures
at present. These treatments are not being practiced extensively because
they are tedious and difficult to apply under usual farm conditions. They
also require close temperature control, and wet the seed during treatment.
Generally speaking, they reduce germination, retard emergence and decrease
yield. These treatments have been carried out satisfactorily in some areas

on a community basis under the supervision of an agricultural specialist.

-2-

There seems to be a tendency on the part of the grower to under-
estimate the importance of losses from loose smut. There are two factors
responsible for this. First, loose smut is inconspicuous at harvest time
and therefore cannot be appreciated by the grower. Secondly, the milling
quality of the wheat is not affected by the presence of loose smut as it
is by the presence of other smuts of wheat. Therefore, the losses from
loose smut are field losses and not market losses.

This study is a continuation of earlier research on the development
of a dry heat treatment for the control of loose smut in.wheat. Its
primary purpose was to deveIOp a method which would lend itself to large

scale treatment of wheat.

rfi

REVIEN OF LITERATURE

The Nature of Loose Smut

Loose smut (Ustilago Tritici), is one of the many diseases which
affect. wheat. It differs from other smuts of wheat in that its presence
can be detected only during the flowering stage of the growing cycle. The
smut infected heads emerge from the boot slightly earlier than the normal
heads. They appear as black masses of Spores instead of an otherwise
healthy head of wheat, which upon drying, becomes powdery and sooty.
Sometimes only the lower part of the head is destroyed leaving the upper
part of the head unaffected. But usually, the whole head is infected, and
the glumes and grain completely destroyed.

These black masses of spores are surrounded by a thin membrane which
consists of the infected glumes. This membrane soon ruptures and as the
smut spores dry they are spread about the field by the wind, insects and
other agencies. The greatest hunter of black heads in an infected field
are apparent when the wheat is in.full bloom. As these countless numbers
of spores are scattered and carried about the field, they become lodged
between the glumes of the healthy heads. Inoculation occurs when one or
more of these spores happen to fall on the ovary or stigma which is eXposed
between the glumes when the healthy heads are in bloom. Within a few days
all the smut spores are either blown, carried, or washed from the diseased
heads leaving only the naked rachises of the spikes.

The spores soon germinate and the germ tubes produce a mycelium within
the developing seed. This smut mycelium.soon steps growing and remains
dormant in the wheat kernel. When the infected seed is planted and growth

begins, the dormant mycelium revives and begins to grow along with the wheat.

-4-

Nhen the wheat reaches the flowering stage, the black masses of Spores
appear, and the life cycle is concluded. The deveIOpment of loose smut
at several different stages is shown in Figure 1.

Since loose smut is an internally borne fungus, it can be transmitted
only during the flowering stage of the growing cycle. 'Uhen the plant is
growing, it is impossible to distinguish between an infected plant and a
healthy plant by observation. Likewise, after harvest the affected seeds
appear to be normal. There is no difference in color, size or shape be-
tween the infected and uninfected seed. The structure of the wheat berry
appears in Figure 2. I

It has been found by Tapke (28) that wheat plants infected with loose
smut will winter-kill more easily than uninfected plants. This, of course,
is desirable but the yield may be reduced markedly if the planting rate

is not adjusted to compensate for this loss.

Rapid Method for Qgtection of Looge Smut Myselium.
Pbpp (22) reports the following rapid method for detecting the presence

of loose smut mycelium in seeds and seedlings. ”Before seed embryos could
be prepared for examination, it was necessary to separate them from the
endosperm and pericarp. Kernels were macerated for 48 hours in a 10 per-
cent solution of potassium hydroxide at room temperature. During macera-
tion, the endosperm and embryo became swollen and usually ruptured the
pericarp. The solution and macerated seed were poured into a 10-mesh sieve,
through which the embryos were strained into a beaker with the aid of a
rinse Spray. The solution was then poured off and replaced with a 10 per-
cent solution of potassium hydroxide, and in it the embryos were boiled for

about one minute each time to leach out most of the potassium hydroxide.

 

 

Figure 1.

-5-

 

 

Wheat heads showing appearance
and development of loose smut.

A.
B.
C.

D.

F.

normal head.

Smutted head in the boot.
Smutted head as it emerges.
Stage of spore distribution.
Rachis after spores are gone.

Partially normal and partially
infected head.

 

~6—

Aleurone Inner Inner Layer
Layer Integument of Pericarp Perioarp

. -~.\\§\‘ My -.
my} thigh
"an 1‘39"!“ .

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"up
'% t
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‘ o a o
a
gas/’1 .2 00 do a
[2‘39" 4 ". 'ok‘0 9
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ll:

 
  
 

Starch Cells

or A
Endospern *

Figure 2. Structure of the wheat berry.
A - Wheat berry cut through at the crease.

B - Cross section of the wheat berry.

* The loose snmt mycelium is believed to lie dormant in the
endosperm and/or in the wheat germ.

Tb facilitate the detection of mycelium, the embryos were boiled for
about four minutes in a staining solution.* The treated emtryos were
mounted in rows on glass slides and slightly flattened under a cover glass
for examination under the microscOpe. The mounting medium was a solution
of one part glycerin and two parts distilled water. During treatment, the
embryo tissue became light blue and translucent. The mycelium was more
darkly stained and could be easily recognized in the semitransparent host
tissue. An embryo was considered to be infected if smut mycelium was found
in any part of it."

In the detection of loose smut mycelium in seedlings, only a portion
of each seedling was used. This included the crown node, about 1/8 inch
of the sub-crown internode, and 3/8 inch of the plumule. These were ex-
cised for examination of the growing point after the tip of the second leaf
had made its appearance. The excised pieces were boiled in a 10 percent
solution of potassium hydroxide for about five minutes or until the tissue
became semitranSparent. The seedling pieces were then washed, stained,
mounted, and examined in the same manner as the embryos.

A.modification of this method was employed in the detection of loose
smut mycelium in wheat samples originating from the 1950 and 1951 craps of
Spring wheat variety Illinois 1-128 which-had shown heavy infection in the

field. Results of these tests appear in Table l.**

 

* Lactic acid 12.5 cc.; phenol (at 45-5000.), 12.5 cc.; glycerin, 12.5 cc.;
distilled water 62.5 cc.; and Pbirrier's tlue (cotton blue), 0.01 gm. In
making up the solution, the cotton blue was dissolved in lactic acid and
water, and the other ingredients were then added.

** Acknowledgment is due to Mustapha Zeidan, graduate student in the Depart-
ment of Botany and Plant Pathology, for carrying out this work.

-3.

Table 1. Results of detection of loose smut mycelium in the
seedlings of Spring wheat Illinois 1—128.

 

 

Crap Number of Number of Seedlingg Percent
Slides Total Infected

1950 14 66 11 16.5

1951 10 48 14 29

 

The usual and most reliable method of estimating loose smut infection
in wheat plants is to plant the seed and record the percentage of smutted
plants. Field tests, however, are time-consuming and allow experimentation
only at certain times of the year. For this reason greenhouse culture of
a suitable variety was considered to be of great importance. The afore-
mentioned variety, Illinois 1-128, was found particularly suited for this
purpose because of the high incidence of Spontaneous smut infection and
short growing period. When these desirable properties became apparent,

earlier attempts to utilize Popp's method routinely were abandoned.

Methods of Treatment Previously Used

A number of different methods have been used in the control of loose
smut in wheat. They are (l) the selection of large kernels, (2) the use
of seed more than one year old, (3) the removal of smutted.plants from
the field, (A) the use of clean seed, (5) the treatment of seed with hot
water, (6) the selection of resistant varieties and strains, (7) the treat-
ment of seed with infrared radiation and dielectric heating. Of these
control methods which have been tried, the use of resistant varieties
and strains, which are otherwise desirable, and treatment of the seed with

hot water have proven to be most effective.

Use of Besigtant varieties.
Because of the technical difficulties involved in other control methods,

it would seem that the use of resistant varieties offers the most practical
means of controlling this disease. A.number of varieties have been re-
ported resistant by some and susceptible by others. Only a few varieties
have been consistently reported as showing any marked degree of resistance.
In common wheats the resistance ranged from high susceptibility to apparent
immunity. It has been suggested that apparent resistance in varieties may
be due simply to escape of the disease by virtue of a relatively cleistoga-
nous habit of blooming, to an anthesis of short duration, or to both. Howb
ever, tests conducted by Tapke (30) indicate that this was not the case
but that it was due to something more fundamental in its constitution.

Some varieties are better adapted to certain growing conditions than
others. This is a factor which must be considered before selection of a

variety is made.

-10-

Relative Humidity During Blooming Period.
Loose smut rarely occurs in the Pacific Coast states. It is believed

that the low relative humidity which generally prevails there during the
flowering period might play an important role in.preventing infection (31).
It is quite prevalent in the eastern or more humid areas of the Uhited
States. The loose smut fungus is very much dependent on.moisture for its
existence. Perhaps the Spores are dehydrated to the extent that they

will not germinate when they reach the ovary, in the low relative humidity
regions.

Three varieties which are grown in one or more of the Pacific Coast
states and rarely produce loose smut there, were inoculated under humid
conditions in a greenhouse at the Arlington Experiment Farm, Rosalyn,
Virginia (31). The resulting seed produced from 91 to 98 percent smutted
plants. The percentage of smutted plants was considerably less when they

were subjected to a low relative humidity after inoculation.

Hot Hater Treatments

Modified'Hater Bath Treatment.
Tapke (28) reports the following treatment which is a modification of

an earlier hot water treatment. In the modified hot water treatment, the
wheat is placed in a porous container, usually a burlap sack. The sacks
are only half filled because soaking causes the wheat to swell considerably.
The sacks are then tied at the top.

The wheat is then.presoaked for 4 to 6 hours in unheated water. It is
then dipped.momentarily in.water heated to 49°C. to warm the seed and then
soaked for 10 minutes in water maintained at 54°C. Finally, it is either
ddpped in cold water or spread in a thin layer without dipping in cold

water and allowed to dry and cool.

§ingle Bath Treatment.
In the single bath hot water treatment, the initial 4 - 6 hour period

of presoaking is omitted. The seed is soaked for one hour and fifty minutes
in water at a temperature of 489C. or for one hour and thirtybfive minutes
in water at a temperature of 49°C. The seed is then spread in'a thin

layer and allowed to cool and dry. During the presoaking period in the
modified hot water treatment and throughout the single bath treatment, the
sacks should lie on their sides. They should be turned over occasionally

to prevent caking of the swelling wheat.

§team Bath Treatment.
Thpke (28) reports the following steam bath treatments. The wheat is

first soaked for four hours in unheated water. It is then.placed in a small
forced air drier which is equipped to circulate a saturated atmOSphere of
constant temperature. Constant temperature of the saturated air is main~
tained by using steam of temperatures between 26° and 48°C. The length
of treatment varies from one to five hours depending on the temperature_
used. The wheat is then dried by forced air. '

Some of the steam treatments were effective in controlling loose smut
without material injury to germination or reduction of yield. However,
the application of steam treatments to large quantities of wheat would in-

volve difficulties not encountered in the smaller experiments.

Limitations of the Hot Eater Treatments.
The hot water treatments are difficult and tedious to apply. They

involve long periods of time for treatment. Also, during hot water treat-
ments the wheat becomes wet and swollen. This introduces the problem of

drying the wheat. This procedure is rather tedious and eXpensive in that

-12.

it involves time, space, labor, and some risk of loss of seed wheat through
sprouting or freezing. The drying process could be omitted if the seed
is sowed as soon as its surface is dry. Seed in this condition.would
still contain enough moisture to germinate in a dry soil. However, if the
soil remains dry after germination, some of the seedlings may die and the
stand may be severely injured. If the seed is planted when swollen, it
is difficult to adjust the rate of seeding and a thin stand.may result.
The effectiveness of these three treatments is dependent upon very
close temperature control. If the temperature is not closely controlled,
the damage resulting from the treatment may be even greater than that
resulting from the loose smut infection. The application of these treat-
ments involves the maintenance of a constant temperature for relatively
long periods of time. Special equipment is also required which makes the

application of these treatments impractical for the individual farmer.

The effects of these treatments on germination are dependent on the
physical condition of the seed coat. Mechanical threshing usually results
in some broken, cracked, or scratched seeds.‘ When the seed coat is broken
at definite locations over the endosperm, the germination is somewhat re-
tarded. 'Uhen the seed coat is broken over‘the embryo, the treatment re-
duces germination markedly. These treatments will serve to screen the
defective seeds from the healthy seeds. However, if the percentage of
defective seeds is quite high, there will be a marked loss in germination.
Germination tests of the treated seed should be made prior to planting.
The planting rate can then be adjusted to counteract this loss of germina-
tion.

According to Thpke (28), when the planting rate was adjusted so that

the number of viable seeds was the same for the treated and untreated wheat,

-13-

the untreated seed outyielded the treated seed. This would indicate that
the effect is not confined to germination but may extend into the later

stages of plant growth.
Previous Ekperiments With Infrared Radiation

Preliminary investigations were conducted by Lucas (17) to determine
whether infrared radiation would be effective in the control of loose
smut in wheat. Results from these preliminary experiments indicated that
it may be effective. 1 I

Further research was carried on by Kleis et a1. (16) using the infra-
red treatment. A 250dwatt industrial infrared heat lamp was used as a
source of infrared radiation and was mounted above a canvas belt surface.
Provisions were made so that the height of the lamp above the belt sur-
face could be adjusted. The wheat was placed in a single layer on the
belt surface inside a circle, the diameter of which varied from two to
four inches depending on the size of the sample required. The height of
the lamp above the table was measured from the lower surface of the lamp
to the exposed surface of the wheat. The temperature attained during the
treatment was measured by means of a butt~welded thermocouple made from
No. 30 capper and constantan.wires. Small holes were drilled longitudi-
nally through kernels of wheat and one kernel of wheat was strung on the
thermocouple wire until it was directly over the thermocouple. This ker-
nel was then.placed near the center of the single layer of wheat. Several
kernels were strung on either side of this kernel to shield the thermo-
couple from direct radiation. The millivolt potential across this thermo-
couple was measured by means of a Leeds-Northrup potentiometer. Millivolt

readings were then converted to degrees centigrade. At the beginning of

-14,

the treatment the wheat was placed below the lamp on the canvas belt and
the lamp was turned on. After a desired temperature was reached, as
measured by the thermocouple, the lamp was turned off. The sample was then
allowed to cool slowly to room temperature.

Treliminary germination tests were conducted with loose smut infected
wheat to determine the critical temperature above which the germination was
greatly reduced. The wheat was treated at various lamp heights. After this
was done several samples were treated at temperatures above and below this
critical temperature for field planting, to determine their effect on the
loose smut fungus.

Two varieties of wheat were used for the field tests. They were
American Banner and Goens. The height of the lamp above the belt was 10”
for the field tests and the severity of the treatment was regulated by
varying the time of exposure. The temperatures attained during the treat-
ment of American Banner were 78°, 80°, 82°, 84°, 86°, 88°, and 90°C. For
Goens they were 75°, 77°, 79°, 81°, 83°, 85°, and 87°C.

The 90-degree temperature was effective in controlling loose smut in
the American Banner. However, the percentage of emergence and winter sur-
vival of the 90-degree sample was considerably lower than that of the con-
trol. There was evidence of loose smut in all other treatments. The
percentage of loose smut was lower in all cases than the control, which
was 7.6 percent.

The 87-degree treatment was effective in controlling loose smut in
the Goens wheat. There was, however, only 1.9 percent of loose smut in
the control sample.

The results of these infrared treatments appeared quite favorable but
further investigations were necessary before a satisfactory treatment could

be develOped.

-15-

Treatment By Dielectric Heating

Dielectric heating (15) was used as a treatment for the control of
loose smut in wheat because it was believed that it might have advantages
over other methods of heating. Heat is generated within the material to
be heated and would therefore tend to create a uniform temperature through—
out. Also, the wheat could be treated in larger quantities of considerable
thickness.

The source of power used was a.Westinghouse industrial radio frequency
generator with a rated capacity of one kilowatt. It was adjusted to oscil-
late at 10 megacycles, which is its design frequency for dielectric heating.
The wheat was contained by a light cardboard retaining ring. The diameter
of the ring was 4.78" and it was 1” high. On each side of the cardboard
ring was a circular plate made of galvanized iron and 9" in diameter. Each
circular plate was mounted on-Q" insulation board and-Q“ plywood and
connected to the lead terminals. A

The temperature within the sample was measured by means of a capperb
constantan thermocouple made of No. 30 wires. It was inserted through a
small hole in the cardboard ring middway between the galvanized iron plates.
The millivolt potential was measured with a Leeds-Northrup potentiometer
and converted to degrees centigrade.

The variety of wheat used in the dielectric heating experiments was
Illinois 1-128, a spring wheat. One-half pound of this wheat was used for
each treatment. This was placed in the cardboard retaining ring and the
thermocouple was placed approximately in the center of the sample. The
power was turned on, and the current passing through the wheat was adjusted

to two amperes for all tests with dielectric heating. 'Hhen a.predetermined

—l6-

temperature was attained within the sample, the power was turned off. A
second temperature measurement was made sixty seconds after the power was
turned off because of interference by the electrostatic field on the initial
temperature measurement. The second temperature reading, called the 60-
second temperature, was used because of the closer relationship between
this temperature and thus of exposure.

A.nmmber of germination tests were conducted to determine the critical
germination temperature as previously discussed. It was found to be 90°C.
This is several degrees higher than was found for the same variety of wheat
treated with infrared radiation. A.number of samples of loose smut in-
fested wheat were treated at a temperature both above and below this criti-
cal temperature and.planted in the field to determine the effect on the
loose smut fungus. One hundred kernels from each treatment were taken
from the center of each sample and hand planted in rows so that counts
could be made later. The remainder of each sample was drilled in the field
for comparison.purposes. -

Sixty-second temperature treatments of 99°, 96.20, 95°, and 93.800.
showed no smutted heads in the hand planted plots. This was not substan-
tiated by the drilled plot. The emergence, in most cases, was very low
where no loose smut was evident.

In view of the inconsistency between the temperature readings and
field results for the same replication, it appears that this method of
treatment needs further study. One definite disadvantage of dielectric

heating is the high cost of the dielectric heating equipment.

-17-

TREATMENT WITH INFRARED RADIATION

Objectives

The results of previous investigations (15, 16) indicated that infra-
red radiation may be effective in the control of loose smut. It is be-
lieved that the margin between the temperature which affects the wheat
germ and the temperature which affects the loose smut fungus is suffi-
ciently wide to permit this treatment. Further research.was necessary
however, to determine the Optimum exposure time and lamp height which
would effectively control the loose smut fungus without causing a marked

reduction in the percent of emergence.

The Nature of Infrared Energy.

Infrared energy is one form of energy in the electromagnetic Spectrum.
The infrared band in the Spectrum is relatively wide and lies between the
visible and radio bands. The wave length varies from 7600 to 1,000,000
Angstrom units (Figure 3). Generally speaking, the shorter wave lengths
within this region, have the ability to penetrate, and this infrared radia-
tion is readily converted to heat energy.

Radiation waves travel with a velocity V, which depends upon the
medium through which they are prOpagating. The frequency of radiation, f,
is dependent only on the source and does not vary with the medium. The
ratio Y/f = L is called the wave length of the radiation. The wave length
depends on the medium through which it is prOpagated as well as the

source (4).

figctors Affecting Absorption and Reflection.
When radiant energy falls upon a body, part or all of it may be

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-19-

absorbed, part or all of it may be reflected, and part or all of it may
be transmitted. Most solids are Opaque to nearly all thermal radiation.
Consequently, the absorption takes place within a very thin surface layer.
An opaque body is a body which will absorb or reflect all of the radiant
energy incident upon it. ‘Wheat is considered to be opaque. Therefore,
none of the incident radiation will be transmitted. All of it will be
either absorbed or reflected. The total incident radiation will then be

equal to the absorbed radiation.plus the reflected radiation (4).

qa + qr = qt (1)

or if q
—E» = a and '2: = r
Qt qt

then a + r = l

where: a = absorptivity, or fraction of the incident radiation
absorbed,
and r = reflectivity, or fraction of the incident raidation

reflected at the surface.

It can be seen from equation (1) that as the absorptivity increases,
the reflectivity decreases and as the reflectivity increases the absorpti-
vity decreases. The values of a and r vary with the wave length of the
incident radiation. The wave length.most readily absorbed by a body is
affected by the temperature of that body.

A gray body is one which has a constant absorption factor, a, for all
wave lengths and temperatures. It is common.practice to use the mean of
the absorption factors for the temperature range involved.

A black body is a body which will absorb all of the radiant energy
incident upon it. Theoretically, its absorption factor, a, is equal to
one. Actually, there are no black bodies. The absorption factor, a, is

defined as the ratio of the amount of radiant energy absorbed by a body to

(‘3

#20-

the amount absorbed by a black body.

The amount of radiation that a body will absorb depends on a number
of factors. In the case of wheat, they are: (1) temperature of the wheat,
(2) color of the wheat, (3) size and uniformity of kernels: (4) surface
finish, (5) moisture content, (6) chemical composition,_(7) amount of
surface area exposed to the radiant energy. The size and uniformity Of
these kernels would probably be most easily controlled, within limits.
This could be done by screening the wheat before treatment to avoid widen
variations within the same sample. Kernels of different sizes which are
given the same treatment would probably reapond differently because of
different rates of heating. Theeother factors would be relatively cOn—

stant for any one sample of wheat.
Apparatus and Equipment

The source of infrared energy was an Rs40, 250 watt, reflectoretype,
infrared heat lamp. This lamp was used as a source because of its simpli-e
city, availability and low cost. The Operating temperature of the tungsten
filament inside this lamp is about 4,000°F. The wave length Of the greatest
amount of energy is 12,000 Angstrom units (Figure 4). The size Of the
samples treated was necessarily small because Of the rapid decrease in
radiation intensity as the distance from the central axis increases
(Figure 5).

This lamp was mounted on an adjustable stand above a flat plywood
surface as shown in Figure 6. The size of each sample treated throughout
this investigation was approximately one hundred seeds. These were placed
in a single layer on heavy folder paper directly below the central axis

of the lamp. They were placed within a 2" circle on the folder paper;

/\

1“

 

100

80q

60‘4

40‘

Relative energy

20‘

 

 

Infra—red energy

 

 

0
O

T— r r ' I T 17 I I T r j

2 4 6 8 lO 12 14 16 18 20 22 24
wavelength - Angstroms - Thousands

Figure 4. 'Havelength distribution of a
250dwatt infrared heat lamp.

 

100

Q
U!
1

Relative energy
N
‘1‘

Percent of maximum
O:
‘?

 

 

 

O
O

I F— l

’2 ‘6 6 8 10 12

Inches from.1amp axis in a
Elias perpendicular to lamp
3

.1

Figure 5. Energy distribution of a
250~watt infrared heat lamp.

 

-22..

 

 

-23-

guides were constructed on the plywood surface to insure the same place-
ment of each sample under the lamp. One end of the folder paper was
shaped in the form of a funnel to facilitate rapid transfer of the wheat
into a temperature measuring device immediately after the treatment.

The temperature measuring device consisted Of a cylinder of finely
granulated cork, 2 inches in diameter and 2 inches long, set in a small
wooden block. See Figure 7. Cork was used because of its low absorpti-
vity. A.3/4" hole, 1%" deep was drilled into the center of the cork
cylinder. After a sample was transferred to the temperature measuring
device, a cork stOpper was placed in the hole to prevent a rapid loss of
heat from the wheat to the outside air.

The temperature was measured.ty means of a butt-welded thermocouple
made from No. 24 copper and constantan wires. This thermocouple was
centered in the lower portion of the cylindrical cavity as indicated in
Figure 7. A light sheet metal strap was fastened to the cork stOpper by
means of a small screw. This fit comfortably over the left forefinger
and facilitated rapid placement of the stOpper in the hole after the wheat
was introduced. The highest millivolt potential across the thermocouple
was immediately measured with a Leeds-NOrthrup potentiometer. This was
then converted into degrees centigrade, by means of prepared tables.
Temperatures were read to the nearest one-half degree centigrade. The time
required to transfer the wheat into the temperature measuring device was
about 2 seconds. The time required to Obtain the highest reading was
about 20 seconds after the transfer began, and was a function of the re-
action time Of the potentiometer and not the Speed of the Operator.
Figure 8 shows the rate of heat loss from this temperature measuring de—

vice after the highest temperature reading was Obtained.

.24.

 

 

 

 

 

 

é
Ref-'13; __ 4.11214?" g
' ‘° ' fjhg\

\ " {iii

 

 

 

 

 

 

 

Figure 7. Tampera‘hire measuring device used in infrared tests.

Temperature-degrees oentigrade

‘ 1 r

-25-

 

70

65‘

a
‘?

on
O
l

a
‘1

451

 

 

 

q

j
0 8 4 6 8 10

Time-minutes after highest
temperature was measured

Figure 8. Rate of heat loss from temperature measuring device.

-26-

This temperature measuring device measures the temperature of the
micro-atmOSphere about the wheat kernels. The temperature readings Ob-
tained are relative. Hereafter, when reference is made to temperature
readings with the infrared radiation treatments, readings as obtained by
this method Of measurement are implied.

The surface of the wheat which was exposed to the infrared radiation
will reach a higher temperature than the surface in contact with the folder
paper. This could result in widely different temperature readings for
the same treatment. However, it is believed that the surface temperature
of the whole kernel and of the dead air spaces between the kernels will
reach an equilibrium temperature very shortly after being transferred to
the temperature measuring device. A voltage adjuster was connected in the
circuit so the voltage to the lamp could be adjusted to 120 volt for all

tests.
Experimental Procedure

The variety Of wheat used throughout this research.was the 1951 crOp
of Illinois 1-128, a fast growing spring wheat having a high susceptibility
to loose smut. Its moisture content was measured by a Steinlite capaci—
tance-type meter. This was found to be approximately nine percent for
the wheat used in all the infrared tests. Each.day before treatment began,
several samples of wheat were heated to temperatures approaching those ex-
pected from the treatments and placed in the temperature measuring device.
This was done to preheat the cup, thereby lowering the temperature gradient
between the wheat and cork which resulted in.more reliable temperature
readings. Except for a number Of preliminary tests, all treatments were

made in a controlled temperature room which.was maintained at 77.5°F.

-27..

This eliminated the initial temperature of the wheat as a factor affecting
the treatment.

A wheat sample consisting of approximately 100 seeds was placed in a
single layer inside the two-inch circle on the folder paper. The lamp was
then turned on for a period of 3 minutes for most tests. The three-minute
time exposure was chosen arbitrarily and the height of the lamp above the
surface was varied. The height of the lamp above the table was measured
from the lower end of the bulb to the surface of the folder paper. After
the threeeminute treatment the wheat sample was immediately transferred to
the temperature measuring device and the highest temperature reading re-
corded. The sample was then placed in a small envelOpe and allowed to cool
slowly to room temperature. Each sample was tested for germination by
placing fifty seeds on moist filter paper in each of two Petri dishes.
Some samples were planted in greenhouse flats for emergence and loose smut

control tests.

Effect of figfface Heating.
After a number of preliminary tests it was found that a change in

the temperature of the plywood surface around the sample affected the final
temperature reading. This was due to the natural convection currents
originating directly above the heated wheat. ’Hhen this heated air above
the sample rises, cooler air is drawn in from the surrounding surface and
cools the wheat. This interfering factor was minimized by turning the

lamp on for one hour before testing began to insure an equilibrium tempera-

ture of the surrounding surface.

petermining Critical Ifeatment.

Ninety—six tests were conducted in an effort to determine a certain

-28..

critical treatment, where a more severe treatment would cause a marked
drop in the germination.percent. The height of the lamp was varied from
4 to 18 inches. Each sample was treated for three minutes. After the
approximate critical height range was determined, the length of treatment
was varied from two to four minutes. A critical treatment was found to
be ten inches for three minutes. Samples were subjected to a more severe
and a less severe treatment by varying the lamp height below and above
ten inches, reapectively, to determine the effect on germination before

planting in the field.

Effect Of figdden Cooling.
It had been suggested that perhaps a sudden cooling of the heated

wheat may have an adverse effect on the loose smut fungus, and a favorable
effect on the embryo of the wheat. A number of tests were conducted to
determine the effect of both a rapid chill and a slow chill on the heated
wheat. The wheat was cooled by placing a small envelOpe containing the
wheat between two pieces of dry ice. A thermometer was placed in the
sample to measure its temperature.

In both the rapid and slow chill the wheat was cooled to 0°C. The
slow chill required twenty minutes, the rapid chill required one and one-
half minutes. These time periods are arbitrary and were determined ex-
perimentally by varying the distance between the sample and the dry ice.
Each treatment was duplicated. The mean germination percentages of
samples subjected to a severe treatment (9" - 3 minutes) and chilled are.
shown in Table 2. The germination result of the slowly cooled sample
shows an increase of approximately 50% over the nonpchilled and rapidly
chilled samples. Because of this encouraging result, it was decided to

include a slowly chilled sample in the field tests.

-29-

Table 2. Effect of sudden cooling after treatment, on germination.

 

 

Lamp
height Time Temperap Germina-
(inches) (minutes) ture 00. Cooling rate tion %
9 3 78 Slowly cooled to room temp. 56
9 3 78.5 Cooled to 0°C. in 20 min. 81
9 3 78.5 Cooled to 0°C. in 1.5 min. 51
Control - - - 94

 

Field Tests

After preliminary germination tests were completed, and a critical
treatment was established, it was decided to conduct field tests on a
number of different treatments to determine the degree of smut control.
Six different treatments were used for field tests. They are shown to-
gether with germination results in Table 3.

Treatment 4 was included in the field tests because it was suggested
that perhaps a greater lamp height for a longer exposure time may have
the effect of dehydrating the loose smut hyphae.

A 6 x 6 Latin Square design was used for the field tests. There were
100 seeds in each plot, making a total of 600 seeds for each treatment.
The 100 seeds were planted in one 16-foot row with an approximate Spacing
of two inches between seeds. The rows were 6 inches apart. Six guard rows
were planted on both sides of the square, parallel to the test rows to

protect against fringing effects.

-30-

Table 3. Effect of varying lamp heights on germination.

 

 

 

Treatment Lamp Height Time Temperature Percent
Number (inches) (minutes) °C. Germination

1 ll 3 66.5 90

2 10 3 72.0 88

3 9 3 77.0 56

4 16 20 57.5 93

5* 9 3 76.5 81

6 (Control) - - - 94

 

* Slowly chilled following treatment.

-31-

Approximately two weeks after planting, emergence counts were made.
About one month later, during the blooming period, counts were made of
the smutted plants. The emergence and smut results are shown in Table 4.

A summary of these results appears in Table 5.

Statistical Analysis of Field Results.
The frequency distribution of each treatment according to its emer-

gence count and number of smutted plants is given in Table 6. The figures
in the body Of the table are the treatment numbers (Table 4) with no
designation being made as to replication. It is seen that treatments 3 and
5 belong to a pOpulation different in emergence counts, from the other

four treatments. Likewise, treatment 2 tends to belong to a second pOpu-
lation as to emergence counts. Treatments 1, 4, and 6 belong to still a
third pOpulation. The percentages of emergence of treatments 3 and 5 are
so low that they were not included in the analyses of variance. The analyh
ses of variance and covariance on treatments 1, 4, and 6 indicate there
were no significant differences between these three treatments in the per-
cent Of emergence and in the percent of smutted plants. (Tables 7, 8, and 9).
Also, there is no relationship between the percent of emergence and the

percent of smutted plants.

Qfscussion Of Field Results.

The percent of emergence Of all treatments was quite low. Because
the emergence of the control was also reduced, this lack of emergence
cannot be attributed entirely to the infrared treatment. A numter Of other
factors may have been the cause of low emergence. The shoots may have
had difficulty in breaking through the soil which was hard, lumpy, and

dry at the time Of planting. “Wheat from the same lot which.was used for

-32-

Table 4. Field test results from infrared treatments.

 

 

Lamp %
Trt. Replica- Height Time Smutted

NO. tion (inches) (minutes) Temp.°C. % Emergence Plants

 

Control 1 - ~ - 59 4
Control 2 - — - 68 5
Control 3 - - - 75 4
Control 4 - - - 64 2
Control 5 - - - 64 3
Control 6 - - - 63 6
l 1 ll 3 66.5 66 6
l 2 ll 3 65.5 55 3
l 3 ll 3 66.5 68 6
l 4 ll 3 66.5 71 4
1 5 ll 3 66.5 59 6
l 6 11 3 65.5 43 4
2 1 10 3 72.0 55 0
2 2 10 3 71.5 29 O
2 3 10 3 71.5 35 l
2 4 10 3 72.0 30 0
2 5 10 3 72.5 31 1
2 6 10 3 72.5 21 O

 

Table 4. (Continued)

 

 

Lamp ' %
Trt. Replica- Height Time Smutted
N0. tion (inches) (minutes) Temp.°C. % Emergence Plants

 

3 1 9 3 76.5 19 0
3 2 9 3 77.5 1 0
3 3 9 3 77.5 6 0
3 4 9 3 77.5 4 0
3 5 9 3 78.5 3 0
3 6 9 3 78.5 2 0
4 16 20 57.5 63 3
4 2 16 20 57.5 58 5
4 3 16 20 57.5 49 2
4 4 16 20 58.0 70 5
4 5 16 20 57.5 54 3
4 6 16 20 57.0 60 3
5* 1 9 3 76.0 3 0
5* 2 9 3 75.5 6 0
5* 3 9 3 75.5 4 0
5* 4 9 3 76.5 1 0
5* 5 9 3 76.5 1 0
5* 6 9 3 76.5 10 0

 

*Slowly chilled following treatment.

Table 5. Summary of field tests.

 

 

 

Lamp Percent
Height Time Percent Smutted
(inches) (minutes) Temperature °C. Energence Plants

ll 3 66. 5 61 4. 8

10 3 72.0 34 .3

9 3 77. 0 6 0

16 20 57. 5 59 3. 5

9* 3 76. 0 6 0

Control - - 66 4.0

 

* Slowly chilled following treatment.

-35-

Table 6. Frequency distribution by treatment number, of field results.

 

 

Perc t
Emergzgce Percent Smutted Plants

 

 

 

 

 

 

Table 7. Analysis of variance of field emergence results.

 

 

 

Source df SS MS F
Thtal 17 928 — -
Replication 5 244 - -
Treatment 2 131 65.5 1.18
Error 10 553 55.3 -

 

F2,10 at 5% is 4.10

Table 8. Analysis Of variance of field smut results.

 

 

____

 

Source df SS MS F
Tbtal 17 32 — -
Replication 5 l - -
Treatment 2 6 3 1.2
Error 10 25 2.5 -

 

F2,10 at 5% is 4.10

-37-

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 9. Analysis of covariance of field results.
Energence Smut
S‘mce df A B c b=B- bB C-bB df
A adja MS
3x2 Sxy Sy2
Replication 5 244 ~12 l - - ... - -
beamentl 2 131 5 6 0038 019 5081 l "
Errorz 10 553 69 25 .125 8.611639 9 v2=1.82
b
F = €2,2- = 1.38% = 4.73 - not significant

191,9 at 5% is 5.12

-33-

field planting was later found to be infected with a fungus, RhizOpus.
This fungus growth may have been aggravated under adverse conditions
such as low night temperatures. The field planting was done under the
supervision of the Farm Crops Department.

The marked reduction in percent Of emergence of treatments 2, 3 and
5, was,undoubtedly, the result of the severe treatments which.probably
killed or damaged the wheat germs, thereby affecting the emergence.

Treatments 3 and 5 were completely effective in controlling the loose
smut fungus. However, the emergence of these two treatments was so ex-
tremely low that this is of little significance. Treatment 5 which was
slowly chilled to 0°C. immediately after treatment resulted in an increase
of about 50 percent in germination over the same treatment followed by
slow cooling to room temperature. However, there was practically no
difference in the percent of emergence of these two treatments. This
would tend to indicate that the wheat germ is damaged by the heat treat—
ment to the extent that the shoot cannot push through the soil. The most
favorable conditions for germination are usually maintained in Petri
dishes. Therefore, a slight resuscitation of the wheat may be noticeable
in a germination test but not in an emergence test.

There was evidence of loose smut in all other treatments. However,
there were only two smutted plants of six hundred in treatment 2. The
emergence Of this treatment was considerably lower than that of the control.
A somewhat lower emergence could be tolerated if there was complete con-

trol of loose smut. The planting rate would need to be adjusted to

compensate for this loss of emergence.

-39..

Factors Affecting Reproduceability of Infrared Treatments

Considerable difficulty had been experienced in duplicating tempera-
ture readings for the same treatment. Before proceeding with any further
field tests it was decided to investigate the reasons for these variations
and determine the practicability of using infrared radiation as a treatment.

It had been hOped that there would be a safe temperature margin be-
tween the killing temperature Of the wheat germ and the killing temperature
of the loose smut fungus. However, the results from the field tests in-
dicate that this margin is very narrow. Throughout all the foregoing
treatments with infrared radiation, the temperature readings obtained from
samples subjected to the same treatment varied as much as‘: 1°C. or more
in some instances. This can be seen in Table 4. variations of.t 1°C.
were the smallest that could be Obtained. This variation could very well
mean the difference between killing the smut fungus and killing the wheat
germ. In.most instances, a higher temperature resulted in a lower germina-
tion and a lower temperature resulted in a higher germination. Following
is a discussion of a number of factors affecting the reproduceabllity of

the infrared treatments.

Afr Currents.
The effect of convection currents originating directly above the

wheat sample on the temperature attained, as previously discussed, was
minimized by turning the lamp on for a period of one hour prior to treat-
ment. Air currents originated unintentionally by the motion Of the Opera-
tor during treatment or just before transferring the wheat to the temperap
ture measuring device also affected the temperature attained. Other air
currents produced by natural drafts, heaters or ventilators in the room

also contributed to this error.

Relative Humidity.
Efforts to duplicate treatment 2 of the field tests actually led to

an investigation of the factors affecting the reproduceability of infrap
red treatment. Samples of treatment 2 were treated for the field tests

on May 6, 1952, in a controlled temperature room. The temperature at-
tained for each of six replications was 72 1.0.5°C. (Table 4). On July 29,
1952, an attempt was made to duplicate treatment 2. The same variety of
wheat was used, at the same temperature in the same room. The apparatus,
equipment, and Operator were the same as before. All the conditions were
exactly the same except the wheat was being treated on a different day.

The highest temperature Obtained after two hours of treating was 66.5°C.
The relative humidity on May 6 was 25.3 percent. On July 29 the relative
humidity was 61 percent. Absorption of the infrared radiation by the
water vapor in the air was immediately suspected. It was decided to conduct
further tests to determine if relative humidity was actually a factor
affecting reproduceability of the infrared treatments.

Since it was recognized that relative humidity was an interfering
factor, temperature measurements at other relative humidities were taken.
Because of lack of time, however, only two essentially different humidity
levels were investigated.

The relative humidity in the controlled temperature room was deter-
mined On different days with a sling psychrometer. Tests were conducted
on four different days using a lamp height of ten inches and varying the
time exposure between three and five minutes. Results Of these tests are
shown in TablelD. The results show relative humidities of 61, 62, and 63
percent to be in close agreement. A.relative humidity of 40 percent re-

sulted in a higher temperature attained after three minutes. Also, an

[u

 

 

 

 

 

 

 

Table 10. Effect of different percentages of relative humidity on
the temperatures attained for a 10—inch lamp height,
and 3-5 minute treatment.

July 29 August 4 August 5 July 31

1952 1952 1952 1952

Time R.H. 61% R.H. 62% R.H. 63% R.H. 40%
(Minutes)
Temperature 0C.

3 66.5 66.5 66 71
3.5 68.5 69 68.5 73
4 69 70 69 73
4.5 71 72 70 73
5 72 72 72 73

 

 

 

 

 

-42-

equilibrium temperature was attained after about three and one-half minutes.
This would indicate that when the relative humidity is lower, there is

less atmospheric absorption which results in a higher temperature attained
in a shorter period of time. This is a seriously interfering factor and
one which will vary from day to day and even from one hour to the next.

Furthermore, it is a factor which cannot easily be controlled.

, Egyo Position.
Results of previous germination tests sometimes indicated widely

varying germination percentages for samples subjected to the same treat-
ment and having attained the same temperature. A factor contributing to
this variation was embryo position. If the wheat was placed under the
lamp with the embryo up, the embryo was subjected to direct radiation from
the lamp. Conversely, if the wheat was placed under the lamp with the
embryo down, it would be exposed to practically no direct radiation and
its chances of survival would be much better.

Several tests were conducted to determine_the effect of embryo posi-
tion on the germination. Samples with all embryos up and all embryos down
were subjected tO a very severe treatment. The samples with embryos down
had a germination of fifty percent greater than those samples with embryos
up. This difficulty might be overcome by keeping the wheat in constant.
motion during treatment to insure that one side is subjected to approxi-
mately the same amount of radiation as the other. This could be done by
using a vibrator.

At this point in the research, two months were Spent on improving
the infrared apparatus and equipment. These improvements were made in

an attempt to eliminate some of the error contributing to the inconsistent

-43-

results. Among the improvements made was the use of a belt surface as a
base instead of the folder paper. A.4" x 5" belt at room temperature was
used for each treatment, thereby eliminating the heated base as a factor.
Also, three thermocouples were inserted in the temperature measuring de-
vice to give a more representative temperature reading. Provisions were
also made for a more efficient transfer of heated wheat to the temperature
measuring device. In spite of all these improvements, inconsistent ger—
mination and temperature results were still in evidence.

In view of the inconsistent results obtained from the infrared treat-
ments and the nature of the interfering factors, it was decided to abandon
the use Of this method of treatment. The interfering factors cannot be
easily controlled. Perhaps a different source of infrared energy would
be more desirable. A lower temperature and more uniform source which is
in direct contact with the wheat from two sides would eliminate relative

humidity, emtryo position and air currents as interfering factors.

-44..

TREATMENT'HITH OVEN HEAT

Objectives

Because infrared treatments could not be accurately reproduced, there
was a need for a source of heat energy which could be closely controlled.
A review of literature revealed the investigations of Caldecott and Smith
(5), and Suskind (27) on the resuscitation of heat-inactivated seeds by
x-radiation. In the experiments conducted by Caldecott and Smith, wheat
was subjected to a lethal heat treatment in an electric oven. The wheat
was then exposed to x-radiation to determine the effect of post-irradia-
tion on the heat-inactivated.seed. Suskind later made an attempt to
duplicate the results obtained by Caldecott and Smith. In attempting to
work with an electric oven, he found the temperatures to vary as much as
a 15°C. from the desired pOint of treatment. Tb overcOme the difficulties
encountered, Suskind used an Abderhalden heating apparatus for the heat
treatment of wheat. Tests were conducted to determine the lethal tempera-
ture of wheat. The same variety of wheat was used in both investigations.
Suskind could not duplicate the observations of Caldecott and Smith.

Results of these previous investigations indicated that wheat would
survive after being subjected to oven treatments using unexpectedly high
temperatures. Because of this interesting fact, it was decided to study
the use of an electric oven as a source of heat for the control of loose
smut in wheat.

Fungus hyphae are very much dependent on moisture for their survival.
There is a definite possibility that extensive dehydration of the loose smut
fungus would harm the microorganism more than the seed of the host plant.
Tb obtain a sufficient drying effect the length of treatment would need to

be increased considerably over that used for the infrared tests.

-45-

The immediate objectives of these oven treatments were to determine:
(1) what temperatures and periods of treatment wheat seed would tolerate
without appreciable loss of viability and (2) whether there was a trend

in the control of loose smut with increasing temperature and length of

treatments.
Apparatus and Equipment

It was necessary to use an electric oven which would give very close
temperature control so that treatments could be accurately reproduced.
After experimenting with several available electric ovens, the Cenco Elec-
tric vacuum Oven was found to be the best answer. This oven is cylindrical
in shape and is surrounded by an oil bath (Figure 9). The oil is heated
by fOur 250ewatt knife-type electrical immersion heaters. Two of these
can be controlled by a thermoregulator. The other two are controlled
manually. Since the oven is heated by the oil, the temperature can be
controlled within very close limits. The oven is equipped with an inner
door and an outer door for sealing the open end. This provides a uniform
temperature inside the oven. It can easily be controlled to within
i 0.5%.

The oven used is about twentybfive years old, and of a type which is
no longer being manufactured. It is, however, in excellent condition and
has operated satisfactorily throughout this investigation. It is equipped
with a vacuum pump for reducing the pressure inside the oven. This was
not used in the oven experiments. All tests were conducted at the exist-
ing atmospheric pressure. Two centigrade thermometers were used to

measure the temperature inside the oven and of the oil bath.

-46-

 

 

Figure 9. Cenco Electric Vacuum Oven.

-47-
Experimental Procedure

The same variety of loose smut infected wheat (Illinois 1-128) was
used for the oven treatments as was used in the infrared tests. Its
moisture content was measured by the Steinlite capacitance type meter
and found to be 8 and 3/1 percent. This was later verified by oven dry-
ing a sample of the same wheat.

Approximately one hundred seeds were used for each treatment. These
were placed on a 4' x 5" piece of cotton belt. Belt was used as a base
because it would lend itself to a continuous system.for large scale
treatment of wheat. After the oven was heated to the desired temperature,
the doors were opened and the belt was placed on a shelf inside the even
as shown in Figure 9. Timing of each treatment began after the even had
again reached the desired temperature. In most instances, this required
about fifteen minutes after introducing the wheat. The heaters were
manually controlled as it was possible to obtain much closer temperature
control than by using the thermoregulator.

Preliminary germination tests were conducted to determine the ap-
proximate lethal temperatures of wheat. Twentybone samples were treated
for one-half, one and two hours at temperatures of 60°, 65°, 70°, 75°,
80°, 85°, and 90°C. Treated samples were allowed to cool slowly to room
temperature. One hundred seeds from each sample were then placed on moist
filter paper in two Petri dishes for germination tests as previously dis—
cussed. ane of these treatments were found to have a killing effect on
the wheat germ.

It was then decided to treat samples for one hour at temperatures

of 92°C. and above at two degree intervals until a lethal temperature was

-48-

reached. Samples were treated for one hour at 104°C. before there was a
marked reduction in the germination.percentage (Figure 10). The germina-
tion of all samples treated for one hour at temperatures of 90°C. and
above was somewhat delayed.

A very critical factor involved in plant survival is root develOpment.
For this reason, the weight of radicles from each sample treated at a temper-
ature above 90°C. was measured. This was used as a criterion in determining
the highest oven temperature to be used for smut control tests. All sam-
ples whose weight of roots was measured were planted in sterilized quartz
sand in Petri dishes. This was done to facilitate removal of the plants
without damage to the roots. After a 72-hour germination period, the roots
from each sample were clipped and weighed. Table 11 shows the weight of
radicles together with germination results of several samples treated at

various temperatures for one hour.

Greenhouse Tests

After lethal germination temperatures were determined, treated wheat
was planted in the greenhouse for a preliminary smut control test.

Table 11 shows a relatively sharp drOp in the weight of radicles from
samples heated at 104°C. for one hour. This is accompanied by a rather
marked drop in germination percentage. Consequently, the highest temperap
ture used for greenhouse tests was 102°C.

It was decided to use treatments of 98°, 100° and 102°C. for one-
half, one and two hours for the smut tests. One control sample plus the
nine heat treated samples made a total of ten different treatments. Three
replications were made of each treatment. These were planted in a ran-

domized block design so the results could be statistically analyzed. The

’3

'100

Percent germination

 

O
O
l

(p
9

701

 

 

 

 

60 j r I I 1 1
Control , 94 90 98 100 108 104 106
Temperature-degrees cent igrade

Figure 10. Effect of temperature on germination of
Illinois 1-128 wheat for a one-hour treatment.

-50-

Table 11. Effect of a one—hour treatment at varying temperatures on
germination and weight of radicles after a 72-hour germina—

tion.period.

 

 

 

Temperature Percent 'Ueight of Radicles
°C. Germination from 100 seeds-gm.
96 91 2.46
98 89 1.96
100 88 1.76
102 87 1.62
104 80 1.26

106 65 1.00

 

-51-

treatment numbers and treatments which were used for greenhouse tests are

shown in Table 12.

Table 12. Treatments for greenhouse tests.

Time

 

Treatment number Temperature 0C. minute§_
1 102 30
2 102 60
3 p 102 120
4 100 30
5 100 . 6O
6 100 120
7 98 30
8 98 60
9 98 120

10 Control - -

 

The samples were planted in a greenhouse bench as shown in Figure 11.
There were 125 seeds in each treatment. These were planted in two rows
across the width of the bench. Row spacing was 4' and seed spacing was ap-
proximately 3/4". Two guard rows were planted parallel to the test rows
to eliminate fringing effects.

Fbur BOO-watt lamps with reflectors operated by an electric timer,
were mounted above the greenhouse bench as shown in Figure 11 to extend
the period of light to approximately 12 hours.

Two weeks after planting, emergence counts were taken. Approximately
two months after planting, smut counts were made. These results appear
in Table 13. The figures in the body of the table are the number of

emerged and smmtted plants from.125 seeds.

-52..

 

Figure 11. Oven treated wheat growing
in a greenhouse bench.

Table 13. Emergence and smut results from greenhouse tests.

 

 

 

 

Replication
1 2 3

Tempera- Time No. of Plants No. of Plants No. of Plants
ture °C. (Min . ) merged anutted Finerged anutted Energed firmtted

Control 123 5 118 6 116 0

98 30 108 2 109 2 111 0

98 60 98 2 110 1 110 1

98 120 103 l 102 l 103 0

100 30 117 3 113 O 106 0

100 60 106 O 99 0 103 0

100 120 103 0 87 O 99 0

102 30 116 2 107 0 84 0

102 60 90 0 84 0 86 1

102 120 91 O 92 0 97 0

 

 

 

 

-54,

Statistical Analysis of Greenhouse Results.

The frequency distribution of each treatment according to its emer-
gence count and number of smutted plants appears in Table 14. The figures
in the body of the table are treatment numbers without regard to replica-
tion. An analysis of variance of the emergence results is shown in Table
15. This indicates that time and temperature were both highly significant

factors in the oven treatments.

Qiscussion of Greenhouse Results.

 

A surmnary of the oven greenhouse results is given in Tables 16 and 17.
The numbers which appear in the body of these tables are the number of
emerged or smutted plants from.125 seeds.

There appears to be a marked drop in the number of smutted plants at
a temperature between 98° and 100°C. and at a treatment length of between
thirty and sixty minutes (Table 17). A similar break appears in the number
of emerged plants, although this is not so pronounced (Table 16). This
tends to indicate that a temperature of 98°C. is not high enough to control
loose smut. Also, there are indications that a thirty-aminute oven treat-
ment is too short to control loose smut. There seems to be a trend toward
a decreasing number of smutted plants with an increase in temperature above

98°C. and an increase in the period of treatment longer than thirty minutes.

-55-

Table 14. Frequency distribution by treatment number, of the results
from greenhouse tests.

 

 

Number of Number of Smutted Plants

Plants
Emerged

 

2

3

4

 

12

17
18

23
24

29
30

35
36

47
48

54
55

61

66
67

72
73

78
79

84
85

91

97
102

103
108

109
114

115
120

121
126

 

1,2
2,6

3,3
3,5,6
1,4,5,5
6,9

4,7

10

 

 

Fl ~: «1 co

 

 

 

10

 

10

 

-56—

Table 15. Analysis of variance of emergence results from greenhouse

 

 

 

 

tests.
df
Source Total Active S. S. M. S. F
Total 29 29 3311 - -
Replication 2 2 93 46.5 -
Treatment 9 - 2374 263.8 5.65**
Control: Others 1 1 849 - -
‘Hithin Others 8 - 1525 191 4.1**
Time 2 2 715 357 7.6**
Temperature 2 2 598 299 6.4**
Time I Temp. 4 4 212 53 1.1
Error 18 18 844 46.7 -
F9,18 at 1% is 3.60
F8,18 at 1% is 3.71
F2,18 at 1% is 6.01

F4,18 at 5% is 2.93

-57-

Table 16. Summary of emergence results from greenhouse tests.

 

 

 

 

 

 

 

 

 

 

 

 

Time
(Minutes) Temperature °C.
98 100 102 Sum
30 108 117 116
109 113 107
111 19.62 131
328 336 307 971
60 98 106 90
110 99 84
112 191 .1352
318 308 260 886
120 103 103 91
102 87 92
192 .22 .21
308 289 280 877
Sum 954 933 847 2734 2734
Control 123
118
119
357
Tbtal 3091
Table 17. Summary of smut results from greenhouse tests.
Time
(Minutes) Temperature °C.
98 100 102 Sum
30 4 3 2 9
60 4 0 1 5
120 2 0 O 2
Sum 10 3 3 16 16
Control 11
Total 27

-58-
SUMMARY

The various hot water treatments are the only generally recommended
methods of treatment for the control of loose smut in.wheat. The disad-
vantages of using these treatments are: (1) the seed is wetted during
treatment, (2) close temperature control is required, and (3) they are
difficult and tedious to apply.

A.dry heat treatment for the control of loose smut in wheat would be
very desirable. This investigation.was directed toward the development of
such a treatment.. Dry heat treatments which were employed in this study
were infrared radiation and heat generated in an electric oven. Results
from the infrared tests indicate that this method of treatment might be
effective if it could be controlled more closely. Several factors were
found to be impairing the accuracy of the infrared treatments. They are,
a difference in the degree of embryo exposure in the various samples,
atmOSpheric absorption of some of the infrared radiation, and the effect
of air currents during treatment.) Since these interfering factors are of '
such a nature that they could not easily be controlled, it was decided to
abandon the use of infrared lamps as a source of heat.

Infected seed was treated in an electric oven and planted in a green-
house to determine the degree of loose smut control. Results from the
greenhouse tests indicate a trend toward decreasing incidence of loose
smut after treatment at temperatures above 98°C. and treatment periods of
more than thirty minutes.

Tests on a larger scale will be necessary to determine the Optimal
conditions under which such a treatment is practicable. Such a treatment,
if standardized, will lend itself to a continuous process for large scale

treatment of wheat.

1.

2.

3.

4.

5.

7.

8.

9.

10.

11.

12.

13.

15.

16.

-59..

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. Forecasting loose smut in wheat. North Dakota

 

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Caldecott, R. 8., and L. Smith. Resuscitation of Heat Inactivated
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Canada, A. H. Infrared, Its Military and Peacetime Uses. General
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-60-

Lucas, EL H. Oral communication, 1952-1953.

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Ibpp, H. Infection in Seeds and Seedlings of Wheat and Barley in

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___. Nheats Highly Resistant to Loose Smut. United States
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__. Hheat loose smut infection prevented by arid climate.
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I

Will

mumnmm

93 03046

HI

312